Recovery of oil from oil reservoirs

ABSTRACT

This invention relates to a process for recovery of oil from oil reservoirs with assistance from microorganisms. More particularly, the present invention contemplates a method for recovering oil from a reservoir comprising increasing the population of endogenous microorganisms in said reservoir, said microorganisms having surface active properties, to a level sufficient to effect enhanced oil recovery.

This invention relates to a process for recovery of oil from oilreservoirs with assistance from microorganisms.

During primary oil production, the pressure within a reservoir decreaseswith a subsequent decline in oil production. To compensate for thisproduction decrease water or gas is injected into the reservoir. Thisprocess is referred to as secondary oil production. During secondaryproduction, the water to oil ratio increases until oil production is nolonger economical. The residual oil, up to 65% of the original oil inplace (OOIP), is distributed in a significantly different pattern to theOOIP. The failure of secondary oil production procedures to releasetrapped residual oil results from capillary forces in the oil/water/rocksystem and the failure of injected fluids to penetrate parts of thereservoir formation. Surfactants are used to lower the interfacialtension between reservoir fluids and residual oil so that oil whichcannot be removed by the injected fluids alone is displaced. Surfactantsused in chemical EOR (enhanced oil recovery) show optimal activity overa narrow range of temperature, HLB (hydrophobic lipophilic balance)values, salinities and rock types. Thus, surfactant EOR processes aregenerally developed for individual reservoirs.

Surfactants derived from crude oil (e.g. petroleum sulphonates) havebeen shown in some field pilots to strip out residual oil but at a costmuch higher than the market value of the oil recovered in this way. Thesurfactants are themselves expensive: they tend to adsorb to rock, andso large quantities are needed. Polymers, too, have had some successes,but again at a high cost. Both polyacrylamide, made from petroleumfeedstocks, and the microbial product xanthan gum have been used: theformer is less expensive but is not effective at the high temperaturesand salinity levels common in many reservoirs. The latter is technicallymore satisfactory though there are problems of microgel formationcausing blocking at the injection face, degradation may take place inthe reservoir and, once again, the material is expensive.

It has been proposed to use microorganism derived surfactants for EOR.This technique is known as microbially enhanced oil recovery (MEOR).

The production of surface active agents by microorganisms has beenrecognised for a number of years. These biosurfactant compounds almostuniversally contain a lipid component and are usually glycolipids. Otherclasses of biosurfactants are lipopeptides, phospholipids, fatty acidsand neutral lipids.

There are several potential advantages in using MEOR processes. Theseinclude, the wide range of compounds with useful properties for EOR thatcan be produced by microbial biosynthesis, cost, and the ability toproduce biometabolites within the reservoir and thus decrease the amountof chemical surfactants required.

Current MEOR techniques have involved the injection and establishment ofan exogenous microbial population in an oil reservoir. This populationis supplied with nutrients such as molasses or other fermentable sugars,a source of nitrogen and mineral salts as additives to the water floodemployed for secondary oil removal. Other hydrocarbon substrates havebeen researched, however the economic advantage of fermentable sugarshave made them the preferred substrate.

The development of methods utilizing the injection of microorganismsinto oil reservoirs has been limited by the conditions which prevail inoil reservoirs. In particular, small and variable reservoir pore sizestogether with extremely high temperatures, salinity/ionic strengths andpressures have severely limited the type, range and number ofmicroorganisms that can be injected. Further, and of equal significance,is the highly reduced environment present in many reservoirs. Theabsence of oxygen severely limits the range of biometabolites that canbe synthesized by organisms introduced into oil reservoirs.

A disadvantage of the microorganisms utilized in current MEOR technologyis that they may tend to occlude the reservoir pores due to their largecell volume caused by the rich nutrient conditions provided in thewaterflood. These large cells may also find it difficult to penetratesmall pores in the rock.

We have surprisingly found that the surface active properties of thosemicroorganisms which are adapted to grow in oil well conditions, may beenhanced by subjecting the microorganisms to nutrient limitingconditions. Such microorganisms are especially useful in MEOR.

Accordingly, the present invention contemplates a method for recoveringoil from a reservoir comprising increasing the population of endogenousmicroorganisms in said reservoir, said microorganisms having surfaceactive properties, to a level sufficient to effect enhanced oilrecovery. Enhanced oil recovery is effected, in one aspect of thepresent invention, under pressure by reducing interfacial tension of oilin said reservoir.

More particularly, one aspect of the present invention contemplates amethod for recovering oil from a reservoir comprising the steps of:

(a) isolating endogenous microorganisms from said reservoir;

(b) ascertaining the limiting nutrient(s) for growth of saidmicroorganisms;

(c) supplying an effective amount of said nutrients(s) to said reservoirfor a time and under conditions sufficient to effect an increase inpopulation of endogenous microorganisms;

(d) maintining said reservoir for a time and under nutrient limitingconditions sufficient to enhance surface active properties of saidmicroorganisms; and

(e)subjecting said reservoir to oil recovery means.

Another aspect of the present invention contemplates a method forrecovering oil from a reservoir comprising the steps of:

(a) isolating endogenous microorganisms from said reservoir;

(b) ascertaining the limiting nutrients(s) for growth of saidmicroorganisms;

(c) growing said microorganisms under conditions sufficient to increasetheir population level;

(d) supplying an effective amount of said nutrient(s) together with saidmicroorganisms to reservoir for a time and under conditions sufficientto effect an increase in population of endogenous microorganisms in saidreservoir;

(e) maintaining said reservoir for a time and under conditionssufficient to enhance surface active properties of the microorganisms insaid reservoir;

(f) subjecting said reservoir to oil recovery means.

According to a further aspect of the present invention, there isprovided a method of enhancing the surface active properties ofmicroorganisms, which comprises subjecting microorganisms adapted togrow in oil well conditions to one or more cycles of growth in anutrient medium followed by nutrient limitation.

In yet a further aspect of the present invention, there is provided amethod of enhanced oil recovery from an oil reservoir which comprises:

(a) providing microorganisms from the reservoir or other source whichmay be adapted to oil reservoir conditions;

(b) placing the microorganisms in a nutrient medium to promote growththereof;

(c) subjecting the microorganisms to one or more cycles of nutrientlimitation;

(d) introducing the microorganisms to the reservoir;

(e) recovering oil from the reservoir.

FIG. 1 is a graphical representation of production of oil in barrels perday (BPD(+)) at Alton-3 well after injection of production water withoutnutrients.

FIG. 2 is a graphical representation of production of oil in barrels perday (BPD(+)) at Alton-3 well after injection of production water withnutrients.

The invention may particularly be practised by removing a sample ofmicroorganisms together with a sample of the liquid within the reservoirin which the microorganisms are resident, and analysing the liquid topredetermine likely growth limiting nutrients. "Nutrients" is used inits broadest sense and includes inorganic or organic compounds requiredby a microorganism for growth or which facilitates growth. Inorganiccompounds contemplated herein includes those containing at least one ofthe following elements: C, H, O, P, N, S, Mg, Fe, or Ca. By way ofexemplification only, such inorganic compounds include PO₄ ²⁻, NH₄ ⁺,NO₂ -, NO₃ -, and SO₄ ²⁻ amongst others. Once determined, thenutrient(s) found to be limiting are then added to the reservoir for atime and under conditions to permit growth of endogenous microorganisms.

At the time of sampling, the amount of assimilative organic carbon isalso determined. More particularly, the reservoir is sampled todetermine if, once a limiting nutrient is supplied, the endogenousmicroorganism could grow and obtain carbon and energy from endogenousorganic compounds. Standard techniques in the art, such as,spectrophotometry, N.M.R. infra red , HPLC, gas chromatography, chemicaltests, and the like, are used to determine the available carboncontaining compounds. If required, a carbon source is supplied alongwith the limiting nutrient. In a preferred embodiment, a non-glucosecarbon compound is used since the glucose and compounds comprisingglucose units (e.g. molasses), have been found not to enhance thesurface active properties of the endogenous microorganism followingtheir growth on such compounds. An example of a preferred non-glucosecarbon source is peptone and the like.

Further, an assessment may be made as to the numbers of microorganismspresent. If a large number of microorganisms is present, it is possiblethen to simply add the missing nutrients directly to the reservoir tostimulate growth for a period of time. On the other hand, where thereare only a small number of microorganisms present, the microorganismsmay be grown such as in the laboratory or, where appropriate, on site,in an appropriate medium in which the missing nutrients are provided, inorder to increase the numbers thereof. It is particularly preferred ifthe microorganisms are subjected to more than one cycle in whichnutrients are added to effect growth, followed by subjecting themicroorganisms to conditions in which they are again nutrient deficient.After this procedure, the microorganisms are introduced to thereservoir. During each aforementioned cycle of growth promotion andgrowth inhibition, analYsis may be performed to determine whether themicroorganisms are in a state of growth. Analysis of fatty acidconfiguration by HPLC or GLC is particularly convenient as the degree ofsaturation and cis/trans configuration of membrane lipids appears toalter as growth is retarded in response to nutrient limitation.

Prior methods of enhanced oil recovery using microorganisms are derivedfrom the assumption that certain strains of microorganisms areinherently more suited to the production of surfactants than others andthat what is required is to isolate from among all of the knownmicroorganisms those best able to produce surfactants. On the otherhand, the present invention is based on the realisation that surfactantproperties are an inherent or induceable characteristics ofmicroorganisms within oil reservoirs, and that surface active propertiesare dependent upon the physical condition of the microorganismsthemselves. Therefore, by surface active property is meant the propertyof a microorganism which reduces surface tension and said property maybe endogenous or exogenous to the cell and may include the production ofa surfactant. Microorganisms may not only possess surface properties,but may also cause gas production which may facilitate oil recovery.Furthermore, with the prior methods, the introduced microorganisms maynot be well suited to survival in the particular environment of thereservoir in question, which environment differs very considerably interms of for example, temperature, pressure, acidity or the like. Thus,the prospects for successful propagation of the microorganisms throughthe reservoir are not good. In a preferred aspect of the presentinvention, where use is made of microoganisms already exiting in thereservoir, it is known from the beginning that these are capable ofsurviving in the environment of the reservoir so that, when returned,they can be expected to survive and to do so without serious risk ofadverse environmental sequences attendant upon the introduction ofexogenous microorganisms.

Generally too, it will be the case that microorganisms within an oilreservoir are in a nutrient deprived state, since conditions in oilreservoirs are generally not conducive to the thriving of amicroorganism population. The microorganisms occupY the boundarY betweenoil and water phases within the reservoir and will be physically locatedaround that boundary in accordance with whether they are nutrientstarved or not. As nutrient deprivation sets in, we have found that themicroorganisms become more hydrophobic. This effect is associated in afashion not fully understood with the surfactant-like properties of themicroorganisms. On the one hand, it is possible that the microorganismwill in this condition manufacture and secrete surface activesubstances, or the cells of the microorganism may themselves assume ahydrophobic or surfactant-like character. Thus, the microorganism cellsthemselves, viable, dorment or possibly after death of themicroorganism, will become the surface-active agent.

In the case where a sample, on analysis after removal from an oilreservoir, is determined as having numerous organisms (i.e. greater thanabout 10³ cells per milliliter), it is assumed that there are sufficientorganisms in the reservoir to provide adequate surfactant productionwhen practicing the invention. In that instance, those nutrients whichlimit microbial growth are supplied to the reservoir, whereafter themicroorganisms are subjected to at least one cycle of nutrientlimitation (by allowing the microorganism to deplete nutrients followedby supply of the depleted nutrients) whereby the surface activeproperties of the microorganisms are increased and oil recoveryenhanced.

In practising the method of the invention where microorganisms areremoved from an oil reservoir and subsequently returned to facilitateoil recovery, the removal of the microorganisms from the reservoir maybe carried out in any conventional manner. Normally, a sample isretrieved from the reservoir via the well casing. The sample includesthe formation water and oil in the reservoir together with themicroorganisms. The retrieved sample is analysed utilizing methods knownper se to persons skilled in the art, for example, atomic absorptionspectrophotometry, to determine the nutrient(s) which appear to belimiting the growth of the organisms. Typically, such an analysis willshow an absence of nitrogen, such as nitrates, and an absence ofphosphates. The organisms are then grown up in a nutrient mediumsupplying the previously determined missing ingredients. Growth of themicroorganisms in a range of nutrient media may be determined, and thatmedium which provides maximal bacterial growth selected formicroorganism culture. During culture of the microorganisms, samples areremoved and tested for surfactant properties. For example, a test may bemade to determine the ability to reduce interfacial- tension as effectedby the organisms and a two-way comparison schedule establishedindicating the relationship between nutrient depletion and resultantsurfactant properties of the organisms. Nutrient depletion may occurnaturally as nutrients are consumed through microbial metabolism or maybe effected by taking the organisms and placing them in a differentmedium, such as placing them in the medium originally withdrawn from thereservoir.

The microorganisms are generally subjected to several cycles of nutrientaddition and nutrient depletion so as to maximise surfactant properties,which can be readily ascertained by measuring a reduction in interfacialtension caused by the microorganisms. Once the desired number oforganisms have been produced which are sufficiently nutrient depleted togive optimal effects insofar as reduction in interfacial tension isconcerned, the organisms are introduced into the oil reservoir. Themicroorganisms may be introduced through the well casing whereafter theyspread from the point of introduction through the reservoir. Themicroorganisms permeate rock pores to act as surfactants to enable thetrapped oil in the rock material to be readily flushed by outgoing waterfrom a well.

It is important to note that microorganisms subjected to cycles ofnutrient addition and depletion have a considerably smaller cell volumethan those microorganisms which are subjected only to conditions ofnutrient addition. A cell volume reduction of 70% is not uncommon.Additionally, such microorganisms may have a smaller cell volume thanthose microorganisms not removed from the well for processing.Microorganisms having a requisite small cell volume are able topenetrate rock pores, which when coupled with the surfactant propertiesof the microorganisms facilitates oil recovery.

Microorganisms which have surfactant properties and are able to survivethe conditions in oil reservoirs, but which are not native to aparticular reservoir in which they are proposed to be introduced, may besubject to cycles of nutrient addition and dePletion to enhance theirsurface active properties in the manner described. Such microorganismsmay then be added to an oil well to enhance oil recovery.

In accordance with the present invention it was surprisingly discoveredthat production water provided an adequate aqueous base in which thedesired nutrients could be dissolved and/or microorganisms introducedprior to introduction into the reservoir. By "production water" is meantthe aqueous phase of an oil-aqueous mixture emitted from a reservoir.Production water may also be referred to as co-produced water. Theproduction water is buffered to be compatible to the ecology of thoreservoir and frequently, carbonate or bicarbonate is used to preparethe buffering conditions. The choice of buffering compound is dependenton the ecological pH of the reservoir which can, in effect, range frompH 2-10. In a preferred method, the desired nutrient(s), optionallyincluding carbon source and/or exogenous microorganisms, are added toproduction water and injected into the reservoir under conditions andfor a time sufficient in accordance with this invention. The emittedaqueous-oil mixture is collected and the phases separated. The aqueousphase is collected and analysed to determine the concentration ofnutrients(s), carbon source and/or microorganisms originally containedtherein. If necessary, the concentration(s) of these additives areadjusted accordingly and the buffering capacity is also adjusted ifnecessary before being injected back into the reservoir where the circleis repeated.

In acccordance with the present invention, it was further surprisinglydiscovered that the order in which the components were added toproduction water made a significant difference to the end result. It isadvisable, therefore, to test individual reservoirs using sandpacks andproduction water to which the components listed in Example 3("Castenholtz" medium) have been added in varying orders.

By reservoir as used herein is meant any locus of deposit. Additionally,"oil recovery means" refers to standard oil recovery practices such as,but not limited to, use of water or gas to generate pressure.

Further details of methods for enhancing surface active properties ofmicroorganisms and the recovery of oil using microorganisms are given inthe following non-limiting examples.

EXAMPLE 1

This example demonstrates the dramatic decrease in interfacial tension(IT) which can be achieved by applying successive nutrient rich andnutrient limited growth cycles. Interfacial tension is measured inmilliNewtons per metre.

A culture of Acinetobacter calcoaceticus with non-detectable surfactantproduction was inoculated into 1/2 strength NB (nutrient broth) with andwithout added paraffin. 1/2 strength NB had been shown in previousexperiments to be optimal nutrient depletion for surfactant production.All cultures were incubated-at 32° C. overnight. The interfacial tensionof the media was then measured against hexadecane using the dropformation method at 24, 48 and 96 hours incubation.

    ______________________________________                                        Media                 Interfacial tension                                     ______________________________________                                        Controls                                                                              1/2 NB            29.56                                                       1/2 NB + paraffin 27.32                                               24 hours                                                                              1/2 NB + culture  30.16                                                       1/2 NB + paraffin + culture                                                                     29.54                                               48 hours                                                                              1/2 NB + culture  26.94                                                       1/2 NB + paraffin + culture                                                                     29.56                                               96 hours                                                                              1/2 NB + culture  29.71                                                       1/2 NB + paraffin + culture                                                                     29.97                                               The culture from the 1/2 NB was then subcultured into                         fresh media and the test repeated.                                            24 hours                                                                              1/2 NB + culture  29.56                                                       1/2 NB + paraffin + culture                                                                     27.32                                               48 hours                                                                              1/2 NB + culture  14.66                                                       1/2 NB + paraffin + culture                                                                     14.04                                               96 hours                                                                              1/2 NB + culture  10.03                                                       1/2 NB + paraffin + culture                                                                      8.60                                               The culture for the 1/2 NB + paraffin + culture was                           subcultured into fresh media and the test repeated.                           24 hours                                                                              1/2 NB + culture   23.25                                                      1/2 NB + paraffin + culture                                                                     20.91                                               48 hours                                                                              1/2 NB + culture  12.25                                                       1/2 NB + paraffin + culture                                                                      9.45                                               96 hours                                                                              1/2 NB + culture  10.12                                                       1/2 NB + paraffin + culture                                                                      6.42                                               ______________________________________                                    

This phenomena was reproduced using a number of mesophilic andthermophilic bacterial species including Psedomonas aeruginosaPseudomonas fluorescens, Bacillus acidocaldarius, Thermus thermophilusand Thermus aquatious.

EXAMPLE 2

This example demonstrates the influence of hydrocarbons in this caseparaffin on reduction in interfacial tension.

A culture of Thermus aqouaticus(T.aq) was inoculated into the media ofCastenholtz (Castenholtz, R.W. (1969), Bacteriol. Rev. 33, 476). Onetube of each pair of cultures was covered with paraffin. The cultureswere then incubated at 70° C. and the interfacial tension measuredagainst hexadecane using the drop formation method.

    ______________________________________                                                     Incubation period                                                Culture      (days)       Interfacial tension                                 ______________________________________                                        T.aq         2            43.96                                                            5            45.41                                                            7            44.97                                                            20           40.28                                               T.aq + paraffin                                                                            2            45.58                                                            5            42.34                                                            7            39.40                                                            20           19.87                                               ______________________________________                                    

Cultures with the lowest interfacial tensions were subcultured to freshmedia and subjected to three further cyles of nutrient limitation andadditio n. The results for the fourth nutrient limitation cycle was asfollows:

    ______________________________________                                                     Incubation period                                                Culture      (days)       Interfacial tension                                 ______________________________________                                        T.aq          6           35.96                                                            11           33.94                                                            28           35.98                                                            32           32.23                                               T.aq + paraffin                                                                             6           33.34                                                            11           28.93                                                            25            8.25                                                            32            5.23                                               ______________________________________                                    

EXAMPLE 3

This example relates to tests effected on a sample of formation waterand oil, retrieved from an oil well known as Alton in the Surat Basin ofSouthern Queensland, Australia.

Sampling Protocol for Reservoir Fluids

I. Samples for Microbioilogical Investigations.

The major objectives during sampling were to collect a specimenrepresentative of the reservoir fluids and to minimize mixing samplewith air. Thus, specimens from Alton were collected from a sample pointat the wellhead using the following protocol.

1. The sample was removed using 50 ml. plastic disposable syringes. Thesyringes were filled completely with sample so that air was notintroduced during aspiration.

2. The needle on the sample syringe was inserted through the rubberseptum of a sample bottle containin g 0.1 ml. of 0.1% resazurin (redoxindicator).

3. A second needle (B) was inserted just through the septum.

4. Reservoir fluids were injected into the sample bottle until theysprayed out through the needle B. When this occurred needle B wasremoved quickly. Subsequently the syringe and needle were removed.

5. Any samples which remained pink for more than 30 minutes afterinjection had 0.2 ml. aliquots of 10% Na₂ S.9H₂ O added until thesolution became colourless.

6. Samples were transported immediately to the laboratory for analysis.

II. Samples for Chemical Investigations.

Samples for chemical analysis were collected according to standardmethodologies, e.g. Collins A.G. (1975), Geochemistry of oilfieldwaters. Developments in sCience series No. 1, Elsevier ScientificPublishing Company, New York.

Initial Assessment of SamPles

I. Microbiological

Microorganims in samples containing oil and water were visualised usingphase microscopy and stains e.g. Gram. A variety of microorganismsincluding a number of highly motile forms were observed. Species weregrouped according to differences in morphology and stainingcharacteristics. The predominant forms were two different bacilli, thefirst was relatively shorter and wider than the second. The shorterorganism on occasions had swollen regions especially in the polarregions, the longer bacilli sometimes formed short chains or clumps. Thethird type of organism was a small Gram positive coccus. The number oforganisms that could be visualized was Proportional to the amount of oilin the sample examined.

II. Chemical

The chemical nature of the oil reservoir water was assessed using anumber of analyses on water and oil/water samPles. These analyses wereconducted using standard techniques e.g. Collins A.G. (1975),Geochemistry of oilfield waters, Developments in science series No. 1.Elsevier Scientific Publishing Company, New York., and AmericanPotroloum Institute (1986).. These techniques include atomic absorptionspectrophotometry (AAS), flame photometery, and the use of selective ionelectrodes. Recommended practice for analysis of oilfieldwaters.Representative of the results of analyses were the following:

    ______________________________________                                        Analysis  mg./l       Analysis   mg./l                                        ______________________________________                                        Sodium    350         Bicarbonate                                                                              800                                          Calcium   3.5         Carbonate   50                                          Potassium 1.5         Chloride   115                                          Magnesium 1.0         Sulphate   4.5                                          Zinc      0.2         Nitrate    0.1                                          Iron      Tr.         Phosphate  Tr.                                          Manganese Tr.         pH         8.4                                          ______________________________________                                         Tr. --Trace                                                              

It was concluded that these results were fairly typical of thoseobtained from fresh artesian water in Lower Cretaceous-Jurassic aquifersin the area of the Surat Basin surrounding the Alton well. Formulationof Bacterial Growth Media:

Several carbon sources were tested for their ability to enhancemicrobial growth in the oil/water samples. These included vayingconcentrations of lactate, acetate, propionate, palmitate, benzoate,formate, hexadecane, hexadecene, C₄ C₆ C₈ mix and H₂ /CO₂ /Acetate. Noneof the carbon sources tested enhanced microbial growth.

From these results and the results of the chemical analyses of the Altonwater sample it was deduced that nitrate and phosphate, potentiallyessential nutrients, virtually were depleted. A series of experimentswas undertaken to determine whether serial addition and depletion ofthese nutrients would result in the production of surface activesubstances. Concurrent studies were undertaken to determine whether theaddition of recognized bacterial growth stimulants such as peptone andyeast extract would enhance the production of surface active properties.Finally, the media exhibiting potentially desirable characteristics weretested for the recovery of Alton oil from porous material.

I. Initial Growth Media

Formulation of the initial growth media was based on the results of thechemical analyses and the previous observation that bacteria in theAlton reservoir required bicarbonate/carbonate buffering.

Materials and Methods

125 ml. Wheaton bottles were filled with 25 ml. of Alton oil and 75 ml.of the media under test. The bottles were then sealed and capped. Asterilized sample of Alton oil was inoculated into unsupplemented mediaas a control. Constituents of the basic media and the supplements addedare shown in Table 1.

                  TABLE 1                                                         ______________________________________                                        Chemical Constituents of Alton Reservoir Fluids                                       Constituent       mg./l                                               ______________________________________                                        Basic media:                                                                            Ammonium nitrate    500                                                       Nitrilotriacetic acid                                                                             100                                                       Calcium chloride (dihydrated)                                                                     51.3                                                      Magnesium carbonate (hydrated)                                                                    40                                                        Sodium nitrate      689                                                       Potassium nitrate   103                                                       di Sodium hydrogen phosphate                                                                      280                                             Trace elements:                                                                         Ferric chloride     0.28                                                      Manganese chloride  2.6                                                       Zinc chloride       0.24                                                      Boric acid          0.5                                                       Copper acetate      0.02                                                      Sodium molybdate    0.025                                           Other nutrients:                                                                        Nutrient            Final Con-                                                                    centration                                                Sodium carbonate    0.5%                                                      Yeast extract       0.1%                                                      Peptone (beef derived)                                                                            0.1%                                            ______________________________________                                    

From these components, four culture media and a control were prepared.All culture media and the control contained basic media and sodiumcarbonate. The supplements added were shown in Table 2.

                  TABLE 2                                                         ______________________________________                                        Initial Formulation of Growth Media                                           Media #       Supplement                                                      ______________________________________                                        1             Trace elements, yeast extract,                                                peptone                                                         2             Yeast extract, peptone                                          3             Trace elements, peptone                                         4             Peptone                                                         Control       Nil                                                             ______________________________________                                    

All bottles were chemically reduced using 0.5 ml. of 0.5% Sodiumsulphide solution and the anaerobic nature of the bottles verified bythe presence of reduced 0.1% resazurin. Incubation temperature was setat about 72° C. which approximates the temperature of Alton reservoir.

Samples were monitored weekly for growth and interfacial tension. Growthwas measured semi-quantitatively using microscopy. Interfacial tensionwas measured against hexadecane using the drop formation technique(Harkins, M.E. and Brown, B., (1919) J. Amer. Chem. Soc. 41, p. 499).This technique involves expelling a sample from a syringe into asolution of hexadecane. The volume of liquid required for drop formationis ascertained, and interfacial tension measured using standardformulae.

Results

There was no significant difference in semi-quantitative growth betweenmedia.

                  TABLE 3                                                         ______________________________________                                        Formulation of Growth Media                                                   Culture                                                                              Initial  Week 1   Week 2 Week 3  Week 4                                ______________________________________                                        Media 1                                                                              22.9     20.1     22.4   22.4    22.5                                  Media 2                                                                              24.5     20.3     23.8   21.5    21.8                                  Media 3                                                                              24.3     19.3     24.8   22.5    21.5                                  Media 4                                                                              24.3     19.4     24.1   21.5    19.1                                  Media  29.3                                                                   (no oil)                                                                      ______________________________________                                    

This pattern is consistent with a nutrient limited state after initialinoculation (lag phase, Week 1) followed by an active growth period(exponential phase, Week 2). A further nutrient limited state occurs onsubsequent proliferation (stationary phase, Weeks 3 and 4). Media 1 and2 were very rich media. Hence, nutrient depletion was only partial atWeek 4 in these media.

Conclusion

1. The addition of yeast extract was detrimental to interfacial tensionreduction in this time frame.

2. The addition of the trace element solution did not enhance microbialgrowth nor interfacial tension reduction.

As a result of these experiments, Media #4 was chosen for oil recoveryexperiments.

Oil Recovery from Sandpacks

The recover of residual oil from sandpacks was investigated as follows:

Materials

    ______________________________________                                        Sand       May & Baker, Batch MX 6210, acid-washed,                                      mediumfine, Sterilized for 10 hrs at 170° C.                           Grain size: not more than 35% passes                                          through a 300 micron sieve, and not more                                      than 20% passes through a 150 micron                                          sieve.                                                             Sand/Oil   5 ml. of oil per 34 g of sand.                                     Media      Media # 4 (as above).                                              Test tubes Pyrex 9827                                                         Seals      Subaseals No. 33 + cable ties                                      ______________________________________                                    

Methods

1. Sand/oil mixture. Sand and oil were mixed in one batch using theratio of 5 ml. of oil to 34 g. of sand. This sand/oil ratio hadpreviously been determined by waterflooding sand until no furtherresidual oil was recovered. Tubes containing the sand/oil mixture werepacked using an ultrasonic bath for 10 minutes.

2. The equivalent by weight of 5 ml. of oil and 34 g. of sand/oilmixture was added to each tube. In addition 22 ml. of Media # 4 with andwithout carbonate was added to each tube. The tubes were capped and thecaps secured with a tie.

3. All tubes were incubated at 72° C in a hot air oven.

4. The amount of oil recovered from the sandpacks was determined by theweight difference of the tube after any oil on the surface of the waterwas removed by syringe.

5. At the completion of the experiment the amount of oil remaining inthe sand was verified by extraction with an organic solvent comprising87% chloroform and 13% methanol in a soxhlet apparatus.

Results

                  TABLE 4                                                         ______________________________________                                        Recovery of Oil from Sandpacks                                                Mixture                                                                              Week 3   Week 6   Week 9 Total % Recovery                              ______________________________________                                        Media  0.775    0.559    0.231  1.566 36.4                                    SDS    1.541    0.029    0.011  1.579 36.7                                    ______________________________________                                    

Discussion

As microbiological enhancement of oil recovery using Media # 4 wasequivalent to that achieved using a commercial surfactant this mediumwas adopted for final testing.

High Pressure and High Temperature Experiments

The final phase of preliminary experimentation was to analyse oilrecovery under simulated Alton reservoir conditions.

Materials and Methods

The recovery of residual oil under conditions prevailing in the Altonreservoir was tested using an apparatus especially designed for thatpurpose. It comprises a metal tube inside a water jacket. The tube waspacked with porous material and sample then sealed. Temperature ismaintained by a circulating system in which H₂ O is pumped through asilicon oil bath and around the water jacket of the core. Temperature isregulated at 73° C. by a thermostat. Initial pressure of approximately5000 kPa, is generated by an Haskell hydraulic pump.

1. Oil and sand as described above were mixed until there was an excessof oil. This mixture was drained and packed into the stainless steelcolumn. The stainless steel column was then transferred into the core ofthe high pressure/high temperature cell. The column was then placedunder pressure and brought up to temperature.

2. Once the packed sand/oil column had equilibrated, the column wasflooded at regular intervals with water. This process was repeated untilno further oil recovered from the column.

3. Media # 4 which had been adjusted to reflect the chemical equilibriapertaining in the Alton reservoir was introduced into the column untilit displaced the water. The column was then sealed and maintained at therelevant temperature and pressure.

4. Samples were removed from the column and oil release monitored. Atthis time the nutritional status of the bacteria is tested and nutrientflooding repeated or withheld according to the result

5. If residual oil was not displaced during this process, the column wasinoculated with an enriched culture of Alton reservoir bacteria whichhave been nutritionally deprived in the laboratory. The column isreleased and steps 4 and 5 repeated until no further residual oil isretrieved.

Media

The media utilised in this test was comprised of production water fromthe Alton reservoir supplemented with the following chemicals.

    ______________________________________                                                  Chemical    g./10001                                                ______________________________________                                        Sol.sup.n A Nitrilotriacetic acid                                                                        100                                                            Na.sub.2 HPO.sub.4                                                                           280                                                            NH.sub.4 NO.sub.3                                                                           1087                                                            CaCl.sub.2.2H.sub.2 O                                                                        51                                                             MgCO.sub.3     40                                                             NaNO.sub.3     69                                                             KNO.sub.3      103                                                            Peptone       1000                                                Sol.sup.n B NaHCO.sub.3   3000                                                ______________________________________                                    

Solution A and Solution B are mixed together, then adjusted to PH 8.4using either concentrated hydrochloric acid or magnesium carbonate. Thepeptone is then added. This media is filter sterilized and preheated to73° C. prior to flooding the column.

Results

The sand/oil mixture was comprised of 751 g. of sand and 123 ml. of oil.During water flooding 98 ml. of oil was recovered. A nutrient flood wasintroduced after 2 weeks.

                  TABLE 5                                                         ______________________________________                                        Recovery of Oil from Reservoir Simulator                                               Week 1      Week 2   Week 3                                          ______________________________________                                        IT (Interfacial                                                                             18.5       12.8     17.1                                        tension)                                                                      pH            9.32       9.45     8.86                                        Oil recovered (ml)                                                                          1.5        3.4      1.1                                         Total oil remaining in column:                                                                     123 - 98 = 25 ml.                                        Oil recovered:       6 ml.                                                    % additional residual oil recovered:                                                               24%                                                      ______________________________________                                    

EXAMPLE 4a

The results of control field test (i.e. production water withoutnutrients) are presented below. The field test was conducted at theAlton-3 well in Queensland, Australia. The results are presentedgraphically (FIG. 1) and clearly show that after shut out in September,1988, production water alone did not result in enhanced oil recovery.

EXAMPLE 4b

A field test was carried out as outlined below, and involved productionwater plus nutrients. Results are shown in FIG. 2.

In general, buffered production water containing the nutrients given inExample 3 was added to the well and the well "shut in" i.e. closed, fora period of about three weeks. At the end of that time, the well wasbrought back into production and assayed for oil production.

    ______________________________________                                        1. INJECTION PROGRAM                                                          ______________________________________                                        (a) Well status                                                               Producing Beam Pump                                                           Production Casing: 7" O.D. (complete string)                                  From bottom to top:                                                                               2 jts 26# J-55                                                               37 jts 29# N-80                                                               43 jts 23# S-95                                                               87 jts 26# J-55                                            Production Tubing: 27/8", 6.5 ppf, EUE conn                                                      J-55 grade                                                 Slotted Liner:     6032 ft to 6063 ft RKB                                                        6073 ft to 6104 ft RKB                                     Plug Back Total Depth:                                                                           6109 ft RKB                                                (b) Programme                                                                 1.0     Move ring onto location. Rig up. Install                                      kill line on annulus side. Kill well                                          utilising bore water.                                                 2.0     Unseat pump. Pull sucker rod string.                                  3.0     Nipple down Xmas tree. Install BOP's c/w                                      27/8" pipe rams.                                                      4.0     Unseat tubing anchor catcher and RIH with                                     27/8" string tag PBTD to confirm presence                                     or absence of fill on bottom.                                                 Note: Completion BHA from last recompletion                                   is as follows: (Bottom to top)                                                        LENGTH    TOP SET AT                                                          (FT)      (FT RKB)                                            3" O.D. Gas Anchor                                                                              25.6'   5972.03                                             Pump Seat Nipple                                                                                 1.56   5970.47                                             27/8" × 7" TAC                                                                            2.56    5967.91                                             190 jts, 2-7/7" Tubing                                                                        5953.31    14.60                                              Printout cancelled by operator.                                               ______________________________________                                         Notes:                                                                        (i) fluid injection at 0.5 bbl/min at 2200 PSIG                               (ii) a total of 15,000 liters (94.3 bbls) of nutrient solution was            prepared. Allowing for 7% tank bottoms, this gave a pumpable volume of        about 86 bbls; 25 bbls was injected while the nutrient mix was optimized,     the remainder was injected over approximately 3 hours after 9-12 hours        exposure to the atmosphere and subsequent pH rectification.                   (iii) all fluid injected into formation was filtered through 28 and 10        micron filters.                                                                8.0 Unseat packer and POOH.                                                   9.0 Recomplete well as per previous completion string.                       10.0 Nipple down BOP's. N/U Xmas tree.                                        11.0 Rig down and move off location.                                          12.0 Rerun sucker rod string. Space out and land pump in PSN. Put well on     pump.                                                                    

2. RESULTS

Shut in was on January 26, 1989 and shut out was on February 17, 1989.

The following results were obtained.

    __________________________________________________________________________    Date  17/2                                                                             18/2                                                                             19/2                                                                             20/2                                                                             21/2                                                                             22/2                                                                             23/2                                                                             24/2                                                                             25/2                                                                             26/2                                                                             27/2                                                                             28/2                                                                             1/3                                 Gross BPO                                                                           156                                                                              148                                                                              156                                                                              143                                                                              143                                                                              129                                                                              128                                                                              129                                                                              122                                                                              120                                                                              120                                                                              117                                                                              116                                 Oil   -- -- -- -- 20 11 13 14.2                                                                             13.3                                                                             13.8                                                                             14.2                                                                             14.5                                                                             14.9                                __________________________________________________________________________

The results clearly demonstrate an enhanced recovery of oil from thereservoir.

The described arrangement has been advanced merely by way of explanationand many modifications may be made thereto without departing from thespirit and scope of the invention which includes every novel feature andcombination of novel features herein disclosed.

I claim:
 1. A method for recovering oil from a reservoir having a population of endogenous microorganisms comprising adding to said reservoir nutrients comprising a non-glucose-containing carbon source and at least one other non-glucose-containing nutrient, said nutrient being growth effective for the endogenous microorganisms, maintaining said reservoir for a time and under conditions sufficient for the substantial depletion of at least one of the added nutrients, wherein the added nutrients and depletion of at least one of the added nutrients results in microorganisms having reduced cell volume and increased surface active properties, and thereafter subjecting said reservoir to oil recovery means.
 2. The method according to claim 1 wherein said other non-glucose-containing nutrient comprises at least one of the following elements: C,H,O,P,N,S,Mg,Fe or Ca.
 3. The method according to claim 2 wherein said other non-glucose-containing nutrient is an inorganic molecule.
 4. The method according to claim 1 wherein the non-glucose-containing carbon source is peptone or protein and/or digests or extracts or sources thereof.
 5. The method according to claim 1 wherein said non-glucose-containing carbon source is eukaryotic and/or prokaryotic cells and/or cell extracts thereof.
 6. The method according to claim 1 wherein said endogenous microorganisms are indigenous microorganisms.
 7. The method according to claim 1 wherein said decrease in cell volume is at least 70%.
 8. A method according to claim 1 wherein an increase in microbail surface active properties is measured by the hexane drop formation method or by hydrophobic interaction chromatography.
 9. The method according to claim 1 wherein said oil recovery means includes increasing the reservoir pressure to eject oil therefrom.
 10. The method according to claim 9 wherein the increase in reservoir pressure is effected by injecting water or gas into or adjacent to the reservoir.
 11. The method according to claim 1 further comprising the addition of exogenous microorganisms to said reservoir.
 12. The method according to claim 1 wherein nutrients and/or microorganisms are introduced into said reservoir in water or oil.
 13. The method according to claim 12 wherein said water is repeatedly cycled into a reservoir wherein one cycle comprises adding to said water the required effective amount of nutrients and/or microorganisms and then introducing same into a reservoir for at time and under conditions sufficient to effect oil recovery, recovering said water from said recovered oil and optionally determining levels of said nutrients and/or microorganisms therein, replenishing levels thereof if required and re-introducing said water containing replenished levels of said nutrients and/or microorganisms into said reservoir.
 14. The method of claim 1 which is carried out under anaerobic conditions.
 15. A method according to claim 1 wherein said non-glucose-containing carbon source is anaerobically degradable.
 16. A method of oil recovery from an oil reservoir which comprises:(a) providing microorganisms from the reservoir or other source which may be adapted to oil reservoir conditions; (b) placing the microorganisms in a nutrient medium comprising a non-glucose-containing carbon source and at least one other non-glucose-containing nutrient said carbon source and other nutrient being growth effective for the microorganisms; (c) maintaining the microorganisms for a time and under conditions sufficient for the substantial depletion of at least one of the nutrients, wherein the nutrient medium and depletion of at least one of the nutrient results in microorganisms having a reduced cell volume and increased surface active properties; (d) introducing the microorganisms to the reservoir; and (e) recovering oil from the reservoir.
 17. The method according to claim 16 wherein said other non-glucose-containing nutrient comprises at least one of the following elements: C,H,O,P,N,S,Mg,Fe or Ca.
 18. The method according to claim 17 wherein said other non-glucose-containing nutrient is an inorganic molecule.
 19. The method according to claim 16 wherein said non-glucose-containing carbon source is peptone or protein and/or digests or extracts or sources thereof.
 20. The method according to claim 16 wherein the non-glucose-containing carbon source is eukaryotic and/or prokaryotic cells and/or cell extracts thereof.
 21. A method for recovering oil from a reservoir comprising the steps of:(a) isolating endogenous microorganisms from said reservoir; (b) ascertaining the limiting nutrient(s) for growth of said microorganisms; (c) growing said microorganisms under conditions sufficient to increase their population level, and thereafter subjecting said microorganisms to nutrient limiting conditions sufficient to produce a reduction in means cell volume to a level compatible with injection into said reservoir; (d) supplying an amount of said nutrient(s) together with said microorganisms to said reservoir for a time and under conditions sufficient to effect an increase in population of endogenous microorganisms in said reservoir, said nutrients comprising a non-glucose-containing carbon source and at least one other non-glucose-containing nutrient, said nutrients being growth effective for the endogenous microorganisms; (e) maintaining said reservoir for a time and under conditions sufficient for the substantial depletion of at least one of the nutrients, the addition of the non-glucose-containing carbon source, at least one other non-glucose-containing nutrient, and the depletion of at least one of the nutrients resulting in a microorganism having a reduced cell volume and increased surface active properties; and (f) subjecting said reservoir to oil recovery means.
 22. A method for recovering oil from a reservoir comprising first increasing the population of endogenous microorganisms in said reservoir by the addition of a growth effective amount of one or more nutrients comprising an anaerobically-degradable non-glucose-containing carbon source and at least one or more inorganic molecules, and then maintaining said reservoir for a time and under conditions sufficient for the substantial depletion of at least one of the added nutrients, the nutrients and the depletion of at least one of said nutrients resulting in microorganisms having reduced cell volume and increased surface active properties, said depletion being measured over time and/or by the increase in a population of endogenous microorganisms having surface active properties and thereafter subjecting said reservoir to oil recovery means. 